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ton. Line pressure through the timing valve moves the overdrive piston into contact with the overdrive clutch. The DIAGNOSIS AND TESTING AUTOMATIC TRANSMISSION Automatic transmission problems can be a result of poor engine performance, incorrect fluid level, incorrect linkage PRELIMINARY Two basic procedures are required. One procedure for vehicles that are drivable and an alternate procedure for VEHICLE IS DRIVEABLE 1. Check for transmission fault codes using DRB T scan tool. 2. Check fluid level and condition. 3. Adjust throttle and gearshift linkage if complaint was based on delayed, erratic, or harsh shifts. 4. Road test and note how transmission upshifts, downshifts, and engages. 5. Perform hydraulic pressure test if shift problems were noted during road test. 6. Perform air-pressure test to check clutch-band operation. VEHICLE IS DISABLED 1. Check fluid level and condition. 2. Check for broken or disconnected gearshift or throttle linkage. 3. Check for cracked, leaking cooler lines, or loose or missing pressure-port plugs. 4. Raise and support vehicle on safety stands, start engine, shift transmission into gear, and note following: a. If propeller shaft turns but wheels do not, problem is with differential or axle shafts. b. If propeller shaft does not turn and transmission is noisy, stop engine. Remove oil pan, and check for debris. If pan is clear, remove transmission and check for damaged drive plate, converter, oil pump, or input shaft. c. If propeller shaft does not turn and transmission is not noisy, perform hydraulic-pressure test to determine if problem is hydraulic or mechanical. ROAD TESTING Before road testing, be sure the fluid level and control cable adjustments have been checked and adjusted if nec- Observe engine performance during the road test. A poorly tuned engine will not allow accurate analysis of trans- Operate the transmission in all gear ranges. Check for shift variations and engine flare which indicates slippage. Slippage indicated by engine flare, usually means clutch, band or overrunning clutch problems. If the condition is A slipping clutch or band can often be determined by comparing which internal units are applied in the various gear 21 - 976 AUTOMATIC TRANSMISSION - 48RE - SERVICE INFORMATION DR/DH |